Furnace control system



NOV. 8, 1938. SWEET 2,136,256

FURNACE CONTROL SYSTEM Filed Dec. 18, 1935 Fi I.

2 Sheets-Sheet l Inventor:

Alva L. S eet, b5

s Attorney.

Nov. 8, 1938. A, L. swEET 2,136,256

FURNACE CONTROL SYSTEM Filed Dec. 18, 1935 2 Sheets-Sheet 2 g i jsAttorney.

Patented Nov. 8, 1938 UNITED sTATEs FURNACE common. srsrau Alva L.Sweet, Schenectady, N. Y., IIIIIIIOI' to General Electric Company on ofNew 05k.

. v/ 14 Claims.

My invention relates to control systems and particularly to furnacecontrol systems having electric ignition. AW 7 7I-n"afiiontemporaneously flled application of W. D. Cockrell, Serial No.55,133, flled December 18, 1935, assigned to the assignee of the presentapplication, there is disclosed a flame detector of the type utilizingan electric discharge device and in which use is made of the fact that aflame possesses a certain rectifying property, that is, the flame is abetter conductor of electricity in one direction than in the other. Theabove mentioned application also relates to a simplified method ofapplying a negative bias upon the control electrode or grid in theabsence of flame and a positive bias when the flame is present in orderto render the electric discharge device conductive in response to thepresence of flame. The flame'dtector itself consists of a multi-elementelectric discharge device having its e lementswin condilttive relationwith the flame through a pair of flame electrodes. Since the fuel supplyis grounded in practically all installations the cathode flame electrodemay .a

be eliminated by simply connecting the cathode to ground. This latterconstruction is shown as a modification in the application.

The flame detector disclosed in the said application performedsatisfactorily in the detection of flames produced by any well knowntypes of fuel ignited by a pilot flame or by some other means such, forinstance, as a match. However, when the device was installed in an oilburner using electric spark ignition of the type in which the ignitiontransformer secondary has its midpoint grounded, and the use of which isdesirable because of the elimination of radio interference, the devicedid not operate satisfactorily. At certain times the flame detectorwould respond substantially immediately to the presence of flame and atother times there would be a relatively long delay before the electricdischarge device would respond. An investigation showed that there wasapparently an excess of positive ions introduced in the flame inproximity to the spark electrodes when ignition first was establishedand that these positive ions tended to charge the anode flame electrodepositively and the grid negatively for a relatively brief period which,however, was of suiflcient duration to cause unsatisfactory operation ofthe flame detector due to the delay before the electric discharge devicebecame conductive. Just what phenomenon causes the excess of positiveions is not known to me at the present time but it may be that theyresult from the spark itself which, upon the break down of theelectrostatic field, is known to produce ion pairs from which othertypes, I propose to place an additionalflame electrode electricallyconnected to the control electrodemndmositioned in thefpath of the flameintermediate the nozzle or pointwhefe the fuel is projected into thefurnace and the anode flame electrode. This additional flame electrodewould thus be intermediate the anode flame elec trode-andtheignitionelectrodes, as the latter are usually positioned near thenozzle andin proximk ity to the fuel stream. Or, looking at thearrangement of flame electrodes in another manner, the additional flameelectrode and anode flame electrode are spaced from the nozzle atincreasing distances in the direction of flame propagation.

By direction of flame propagation .I meanthe general direction in whichthe flame and hot gases of the flame move. Generally, this is in adirection outwardly from the nozzle or source of supply of fuel. Whenthis was done the flame responsive device became very efllclent in itsoperation and responded practically immediately to the presence offlame. It appears that the positive ions present in the flame areprevented from traveling in the direction of the electrode connected tothe anode and are collected upon this flame electrode, which might betermed a shield electrode, connected to the control electrode of theelectric discharge device and thus the control electrode is renderedpositive much more rapidly than would otherwise be the case. Not

only are the positive ions removed from the path of the negative ionsmoving in the direction of the anode flame electrode but they are alsocollected on the flame electrode connected to the control electrode toprovide an additional source of positive bias for the latter. Thus, itis an object of my invention to provide a simple, highly eillcient, andimmediately responsive means for detecting PATENT OFFICE 4 the presenceof flame in the combustion chamber of a fuel burner.

Another object of my invention is to provide a fuel burner controlsystem including a single i electric discharge device for exertingcontrol over certain phases of operation of the system.

Another object of my invention is to provide an improved control systemfor fuel burners emplcying an electric spark ignition system andparticularly a spark ignition system 'of the type employing atransformer secondary winding having its midpoint grounded.

\ Still another object of my invention 'is to pro vide a simple meansfor checking electrical 19! age across the electrodes of the flameresponsive means to render the system unresponsive in case the leakageis such that unsafe conditions would result.

My invention will be better understood from the following descriptionwhen considered in connection with the accompanying drawing and itsscope will be pointed out in the appended claims. In the accompanyingdrawings:

Fig. 1 illustrates a view partially in elevation and partially insection of a heating system and furnace, with a partial representationof the control. f

Fig. 2 illustrates a control circuit embodying my invention.

1 Fig. 3 illustrates a modification of my invention showing the meansfor checking electrical leakage.

Fig. 4 is a cross-sectional view of the flame electrode assembly shownschematically in Fig. 3.

r Fig. 5 is a cross-sectional viewof a modified form of the flameelectrode assembly illustrated in Fig. 4; and A g 1 lectrode assemblyschematically shown in Figs.

- 1 and 2.

y Referring to Fig. 1, reference numeral Q illustrates a furnace of anyconventional type having a combustion climber it and from which a heating medium, such as steam, is led through conduits Ii and if to a heatexchange device, which may be a radiator l3, located in a zone I whichis to be heated. In the closed heating system I have chosen toillustrate in my preferred embodiment, the condensate from the radiatorI3 is led back to the furnace through return conduits l8 and ii. Thetemperature within the zone ll which may be a room, a group of rooms, abuilding, a group of buildings or the like is kept within predeterminedlimits by a thermal responsive means such as a bimetallic thermostat ll.The thermostat may be of any conventional type, for instance, of thetype in which "start and stop contacts are engaged by the thermalresponsive member and from which electrical connections II, I! and 20lead to a control II. The control 2| maybe of the type disclosed in thecopending application of John Eaton, Serial No. 11,100, 'flled March 14,1935, and assigned to the assignee of the present application.Suiiicient control 4 will be hereafter described to completely describethe combustion chamber of a furnace. Posi- 6 tioned on the burner headadjacent the atomizing nozzle 21' are ignition electrodes ll and 8!which are connected to the secondary of a suitable ignition transformerforming part of the main control equipment II by means of electricalconnections 10 82 and 33. Also supported by the burner head are flameelectrodes 34 and II connected by means of electrical connections I. andI! to a flame responsive control device CI in which is incorporated myim roved flame detector, and which I shall describe in detail later.Ext-Heal connections 38, it and ll interconnect controls Ii and 5:.

From the flgure it will be noted that the flame electrodes are sopositioned that time electrode I4 is positioned intermediate flameelectrode ll. the nozzle 21'; and ignition electrodes II and 3|.Inasmuch as the flame is directed downwardly from a nozzle 21' the flameelectrode 3 is at a greater distance therefrom in the direction of flamepropagation than flame electrode ll. 25

The control apparatus will now be described with more particularity inconnection with Fig.

2 of the drawings. ,Similar parts in Figs. 1 and 2 have been given likereference numerals. The room thermostat is shown at I1 and from it leadso electrical connections II, II and 20. A suitable source ofalternating current electricity is illustrated at 22, 23. The maincontrol is illustrated at II, the flame responsive device at 8|, andfrom an inspection of the latter it will be noted that 5 electricalconnections 3' and I1 lead to flame electrodes I4 and", respectively,and that electrical connections II and II and II also ,lead

therefrom. It may be further noted that elec trical connections ii andII unite to"interconnect.e

one of the contacts associated with room thermostat withone of thecontacts associated with the flame detector.

The burner motor 2! is energized from the 'source 22, I! throughelectrical connections 24 noid it is an extended armature member I2provided with a plurality of bridging members adapted to close thenormally open contacts ll, 0 4i and 41. It will be evident from aninspection of the flgure that the aforesaid contacts will be closedsimultaneously upon the energimtion of the solenoid ll. Attached to thearmature mem-' ber 52 by means of a spring connection I! is an 5extended member 54 adapted to open contacts I! and it after a time delaydetermined by the adjustment of a device such as a dash pot II. In orderto prevent continued intermittent energization'of the solenoid I! inresponse to 7 certain conditions, to be described more fully later, Ihave provided means for deenergizing the control after a predeterminednumber of operations if combustion does not occur and for resetting thesame if combustion occurs This time the main operating relay isenergized by means of a notch 99 on the armature 52 of the relay. Ifproper combustion occurs within a desired number of starting operationsthe pawl 59 is moved upwardly 'by a solenoid Oi connected in parallelwith a relay 919! the flame responsive device and the ratchet returns toits initial position. If combustion does not occur continuedreciprocation of armature 52 rotates ratchet 59 until a projection 92carried thereby moves a contact carrying arm 51 to open a pair ofnormally closed contacts 54. A latch member 85 is provided to maintainthese contacts open until manually reset. The normally closed contacts54 are provided in a holding circuit for the solenoid leading from line5i through line 66, contacts 54, line 61, contacts 55, line 68, line 99,

tacts 41 and connectionJL jihe other side of theprimaryisconnected tothe sourceofthesup ply 22 through electrical connections 14, normallyclosed contacts and electrical connection 15. It is obvious that theignition transformer will be energized upon the energization of solenoid50 through the closing of contacts 41 and will be opened after apredetermined period of time by the opening of contacts 58. The

' ignition transformer is provided with a secondary winding 18, themidpoint of which is grounded at 11 in order to eliminate, as far' aspossible, radio interference. Electrical connections 32' and 33 leadfrom secondary winding of the ignition transformer to ignitionelectrodes "38nd 3| P ioned adjacent nozzle 21'. The

latter is grounded as at 19 in order to establish a conductive paththrough ground from the nozzle to the ground connection 19 of the flameresponsive device.

The flame responsive device that I propose to use is of the typedisclosed in the copending application of W. D. Cockrell mentioned abovecomprising an electric discharge device 8i which'is renderedconductive'in response to the presence of flame. The discharge device isprovided with an anode 82, a cathode 83 and. a control electrode or grid94. The device is supplied with proper voltage from any suitable source,of alternating current electricity and 86, which may be connected tosupply lines 22, 23 by means of a transformer 91 having a primarywinding 88 and a secondary winding 89. The cathode is heated through acircuit composed of electrical connections 99' and 9i leading to thetaps on the secondary winding. The anode is connected to the secondarywinding through electrical connection 92, a relay 93, and an electricalconnection 94 in such manner that when the discharge device is renderedconductive, the relay is energized and actuates its associated armaturemember and a movable contact carrying control member 95 from its lowerposition, where the control member is in contact with electricalconnection 99, to its second and upper position where it is in contactwith connection 41. It may be noted at this point that theresettingsolenoid Ii, referred to previously, being connected in parallel to therelay 93 will be energized simultaneously with the latter. In thisembodiment of my invention the position in which the movable contactmember 95 is shown constitutes the start position of the flame detectorand the upper position constitutes the run position, as will be broughtout more fully when the description of the operation as a whole isgiven. In order to avoid as far as posl0 sible the eflect of currentpulsations in the relay 9! I have connected a condenser across it tosmooth out these pulsations which result from the fact that thedischarge device conducts current only every other half cycle.

The discharge device is maintained in a nonconducting condition duringthe absence of flame by the application of a negative bias on the gridthrough electrical connections 91, condenser 9!, electrical connection99, and resistances I90 and II, the latter being in the grid circuit.Condenser 99 serves also to control the length of time required torender the tubemfifi-conducting upon the cessation of combustion, thistime being dependent on the time required for the condenser todischarge. The condenser thus serves to make the flame responsive deviceresponsive only to flame variations of a predetermined character in amanner well known to,

' 34 and 35 are connected to the electric discharge device by means ofelectrical connections 36 and 31 which lead to a point betweenresistances Hill and NH and to the anode side of the transformerwinding. respectively.

The operation of the control system will now be described. Assuming thatthe furnace has ceased operation and that the temperature within zone l4has decreased to a value where heat is required therein, then thethermal responsive element of room thermostat II will move over to itsleft or start position wherein the thermostatic element engageselectrical connection i8. At the same time, due to the fact thatno'flafiehs'present, the electric discharge 4ie' vice ill will benon-conductive becauseof the negative bias on the control electrode, andrelay 93 and solenoid 6i wilLtherefore be deenergized. Thus, the movablecontrol member associated with the relay will be in its lower or startposition, as indicated in Fig. 2. An energizing circuit for the mainoperating solenoid 50 is then closed and it is as follows: from thesecondary winding 48 of the control transformer 46 through electricalconnection 49, solenoid 50, thermal responsive element of thermostat iiin its start position, electrical connection l8-39, movable controlmember 95 in its start position, electrical connections 40 and 68,normally closed contacts 55, electrical connection 61, normally closedcontacts 63, and electrical connections 66 and 5| to the other side ofthe secondary winding 48. Energization of the solenoid 50 results in theupward movement of its associated contact actuating armature 52 and aconsequent c osing of normally open contacts 45, 45' and 41. The closureof contacts 45 results in the energization of the burner motor 26 whichsupplies fuel and air to the burner chamber through conduits 28 and 29respectively. 81- multaneously with the energization of the burner motorthe ignition transformer 10 is energized through a circuit which is asfollows: source 23, electrical connection I3, contacts 41,

electrical connection 12,primary winding" of the 75 transformer,electrical connection ll, normally closed contacts II, and electricalconnection II which leads to the other side 22 of the source of power.Inorder that the motor and ignition transformer will remain energizedwhile the flame responsive device and its associated movtheestablishment of this holding circuit cuts out the room thermostat I1and the flame responsive device.

In my control system, as in most control systems, fuel is supplied tothe burner during the starting period by the motor for a predeterminedlength of time. If the fuel is ignited properly during the startingperiod a further holding circuit including the run contacts of the flameresponsive device for the solenoid II is established. However, if theflame is not produced within the allotted time the burner is deenergizedby the opening of normally closed contacts arranged in the holdingcircuit previously described for the relay 50. In order to simplify thedescription of the operation I shall assume that proper ignition resultiprior ftifthe time that contacts 55 controlling the holding circuit areopened. Then, in response to the presence of flame, the relay 93 isenergized, as will be described more in detail later, and actuatesmovable control member 95 to its upper position wherein electrical lines40 and 4| are connected. The solenoid 50 thereupon is energized througha second holding circuit which is as follows: electrical connections is,contacts 4!, electrical connections 69 and 40,.movao1e control member 95and electrical connection 4|.

It will be seen that the result is that the solenoid 50 will remainenergized as described above.

Simultaneously with the breaking of the aforesaid holding cii'cuit theignition transformer is deenergized through the opening of contacts 56.The ignition transformer, however, may be energized continuously ifdesired by removing contacts 58 and connecting the primary directly tothe source of supply. The continued energization of relay 50 maintainsthe burner motor 26 energized and a combustible mixture will be suppliedto the burner until such a time as the room thermostat l1 reaches itsright or stop position at which time a short circuit is placed acrossthe relay winding 50 by means of the thermal responsive element of theroom thermostat I! and electrical connection 20. Upon the deenergizationof the solenoid winding 50 all the parts return to the position shown inFig. 2 and the burner motor 26 is deenergized until such a time as theroom thermostat again calls for heat.

The operation of my flame responsive device and the manner in which itactuates the movable ode.

Simultaneouscontact member ll from its lower to upper position will nowbe described in greater detail. As brought out above, the controlelectrode. 84 is normally negatively biased so that the discharge deviceII is non-conductive. Upon the appearance of a flame a conductive pathfrom the anode to the control electrode through the flame is formed asfollows: from electrical connection 81 to the flame electrode 35,through the flame to electrode 34 and thence through electricalconnection II, and resistor III to the grid or control electrode N. Theanode flame electrode is also in conductive relation with the cathodethrough the flame, the ground connection ll of the nozzle 21 and theground connection 1| of the cathode-grid circuit. It is obvious to thoseskilled in the art that the discharge device is wonductive only duringthe half cycle when the anode is positive and when the control electrodeis sufficiently positive with respect to the oath- Durlng the half cyclethat the anode is positive the flame electrode ll will have imposed onit the same potential as the anode, and flame electrode 34, due to theconductivity of the flame. will have imposed on it a positive potentialdetermined by the circuit characteristics. This potential is imposedupon the control electrode rendering it more positive with respect tothe cathode'and the discharge "device-will become conductive. there ispresent upon initiation of combustion a transient condition in thefurnace chamber during' which an excess of positive ions is present.These ions are collected on the flame electrode 34 and they aid in theapplication of a positive bias on the grid and their collection in thismanner also aids in the conduction of current from As has been broughtout previously the anode flame electrode 35 to the cathode flameelectrode 34.

The exact explanation of the presence of the positive ions is not knownto me at present but, as stated previously, they apparently result forthe most part from the use of a particular type of ignition. The effectof the rapidly projected fuel particles may also have some bearing onthe creation of these ions as my experience has shown that the flamevelocity has a bearing on the flame current intensity. After a brieftime interval the transient condition subsides and for all practicalpurposes the flame electrode 34 could then be removed from the circuit,i. e., it does not greatly affect the operation of the systemthereafter.

It will be evident to those skilled in the art that my inventionprovides a flame responsive device that is rapid in operation andcertain in its operation. Sensitivity is increased, as is thesensitivity of the flame detector described in the aforementionedapplication of W. D. Cockrell, by utilizing the property of flames toconduct current better in one direction than in the other. Theconduction, as previously mentioned, is better in a direction, oppositeto flame propagation and the current passes through the flame in thisdirection in the system described. Furthermore, the addition of theflame electrode II, which acts as a shield, gives far greater certaintyof operation.

To render the electric device unresponsive to minor fluctuations andallow it to become deenergized only after a time delay I provide thecondenser 98 in the grid-cathode circuit. This condenser is charged sothat its ground side is negative when no flame is present. However,

upon the appearance of a flame a positive charge necessary to dischargethe condenser is flxed by resistors Ill and II", as well as by the sizeof the capacitor itself and the resistance of the discharge device, andconsequently the tube will not become non-conducting upon thedisappearance of flame until the lapse of a certain length oi time.

The operation of the system when flame does not appear within thepredetermined time will now be described. In this event the movablecontact member will not close a circuit be tween connections 40 and Hwithin the specifled time and consequently the main holding circuitdescribed above will not be energized. However,

the initial holding circuit which was also described above will beclosed through contacts 45 but this holding circuit will be opened bythe opening of contacts 55 after a predetermined time interval, asdetermined by the time delay device 51. Consequently upon the opening ofthe holding circuit solenoid 50 will be deenergized and the armaturemember 52 associated therewith will move downwardly to open its variouscontacts. Inasmuch as no heat would be supplied to the zone I4 duringthis starting period, the room thermostat I1 will remain in its startposition in which the thermal responsive element is in contact withconnection I8. If no flame appeared in the furnace the movable contactmember 95 will remain in the position illustrated and the circuitconditions are such that the relay 50 will be energized to actuate itsarmature member 52 upwardly to again close its associated contacts asdescribed above. Each time that the solenoid is energized armaturemember 52 is moved upwardly and its associated notch 60 actuates ratchet58 a single step in a clockwise direction. After a predetermined numberof actuations, three for example, the normally closed contacts 64 areopened by movement of member 63 by projection 62 on the ratchet wheel.The contacts remain open until the latch member 65 and pawl 59 arereleased manually. Upon the release of the latch and pawl the systemwill again recycle the predetermined number of times if combustion doesnot take place.

In the event of the existence of abnormal conditions as, for instance,the existence of leakage paths on the surface or through the support forthe electrodes either across the flame electrodes 34 and 35 or from theflame electrodes to ground, the flame electrode 34 would be inconductive relation with flame electrode 35 and thus a potential wouldbe imposed upon the grid just as though flames 'were present. While thepossibility of such conditions existing is rather remote, the effect oftheir existence may be avoided by the addition of a source ofelectricity between the two flame electrodes of such polarity that eachtime the anode is positive a negative potential would be imposed uponthe control electrode. In this manner the tube would be renderednonconductive during the half cycle that it would be conductive undernormal conditions. Such an the flame electrodes 34 and 35.

\ tion arrangement is disclosed inFig. 3-wherein I have shown a circuitsimilar in all respects to that shown in Fig. 2 with the exceptionthat Ihave added the additional source of potential between the flameelectrodes 34 and II. This source of potential is obtained from anextension of the secondary winding- 88 of the transformer 51 and extendsthrough electrical connection I05 ,to a cylindrical conducting portionI05 placed between The cylindrical conducting portion I06 and the flameelectrodes are maintained inproper spaced apart relationship by asupporting member I01 comprised of insulating material I08 as will bedescribed later in connection with Fig. 4. An outer metallic portion ofthe electrode holding member I01 is grounded as at I08. The operation ofthis system is the same as that of Fig. 2 whenever normal conditionsexist, that is, the discharge device BI is rendered conductive duringthe alternate half cycles that the anode is at a positive potential andthe grid 84 has imposed upon it a potential rendering it positive withrespect to the cathode. Under normal conditions there is no leakage fromthe cylindrical conducting member I05 to the grid flame electrode 34 andthe fact that a negative potential is imposed on the member will notswing the grid negative in the absence of such leakage. However, uponthe occurrence of leakage paths between the electrodes or therefrom toground on the surface of or through the supporting member, which areusually of high resistance, it will be seen that each time the anodebecomes positive, and at which time the electric discharge device wouldbe normally rendered conductive, a negative potential from the oppositeside of the transformer is applied to the control electrode, thuspreventing the electric discharge device from becoming conductive.

In case a leakage path does exist between electrodes 34 and 35 on thesurface of or through the insulating support I09 then, if the electricalconnection I05 and the cylindrical conducting por- I06 surrounding flameelectrode 35 were omitted, the electric discharge device 8| would berendered conductive each time that the anode became positiveirrespective of the presence of flame. With a suitable negativepotential imposed upon the conducting member each time that the anodebecomes positive, then the potential of the grid with respect to thecathode is determined by the magnitudes of the anode potential, thenegative potential and the resistance of the leakage paths from theanode and conducting member to the cathode. With a suitable negativepotential, then when the resistance of the leakage paths reaches apredetermined value, the grid becomes more negative with respect to thecathode and finally the discharge device will become non-conductive. Itmay be noted that if the leakage paths are not on the surface of orthrough the insulating material, as would be the case if the flameelectrodes would be brought into physical contact at their outerextremities, then there will be no leakage from the conducting memberand the electric discharge device will become conducting. However, thepossibility of the flame electrodes coming into physical contact is veryslight when properly designed.

In case both flame electrodes become grounded through leakages paths onthe surface of or through the insulation it is likely that there will beformed at the same time a leakage path directly across the electrodes.If the electrodes become grounded through separate leakage paths thereresults a leakage path across the electrodes through ground and theoperation will be as described above. In case electrode ll alone becomesgrounded through the above described leakage paths, then the conductingmember I will likewise become grounded because it surrounds theelectrode and any ground leakage path will necessarily extend throughit. The anode potential and the negative potential are both imposed uponthe grid through the leakage path to ground and through conductor II andresistors Ill and III to the grid. If the leakage path to ground becomesof sufiiciently low resistance the negative potential is suflicient toovercome the positive potential imposed on the grid and maintain itsufliciently negative with respect to the grid to prevent the dischargedevice from becoming conductive.

When the above described leakage paths are present and the roomthermostat calls for heat the control will function in the previouslydescribed manner to initiate starting of combustion. As soon as flameappeared there would be formed a conductive path from the anode flameelectrode 35 to the grid through the flame to grid flameelectrode 34 andground, but with a suitable negative potential imposed upon theconducting member IM, as described above, the discharge device cannot bemade conductive The flame detector switch will remain, therefore, in itsstart position. After three such starting cycles the switch 64 will beopened and held open by latch I5, thereby preventing further startinguntil the leakage paths are removed.

The construction of the flame electrode assembly forming part of thesystem shown in Fig. 3 is disclosed in Fig. 4 and it consists of theflame electrodes 34 and 35 which are embedded in an insulating materialill. The cylindrical conducting member illi is shown as completelysurrounding a portion of flame electrode 35 and embedded in theinsulating material and held by the latter in spaced relationship to theflame electrodes. A portion of each flame electrode is surrounded by ametallic conducting member lit, the latter also forming a support forthe insulating material I09. Under normal conditions, when no leakagepaths are present, a conductive path exists between the flame electrodesonly when the flame is present. Upon the occurrence oflgakage pathsacross the flame electrodes or from the latter to ground the controlwill be prevented from responding as described in connection with Fig.3.

A modification of the flame electrode assembly is disclosed in Fig. 5.In this case I have dis-' closed practically the same construction asshown in Fig. 4 with the exception that I have replaced the cylindricalconducting member IN by a simple conducting member I II. It will beobvious to those skilled in the art that upon the occurrence of leakagepaths across the flame electrodes or from the latter to ground theoperation will be the same as described in connection with Figs. 3 and4.

In Fig. 6 I have disclosed a flame electrode assembly of the typeutilized in connection with the systems shown in Figs. 1 and 2. Itconsists merely of the flame electrodes II and SI embedded in aninsulating material I" positioned at the top of and within a cylindricalmetallic member III, as described in connection with Figs. 4 and 5.

Various modiflcations may be made in the device and system embodying myinvention without departing from the spirit andandIdesirethereforethatonlysuchlimitationsahailbeimposedthereinsuchasareimposedthepriorartorsetforthintheappendedciaims.

WhatIclaim asnewanddesiretosecure IettersPatent of the United8tates,is:-

proximity to said nozzle for igniting said combustible mixture,andmeansfor controllimsaid connectedtosaidanodaandaseoondelectrode positioned inthe flame intermediate said noaaie and said flrst electrode andconnected toaaid con trol electrode.

2. In combination, a furnace, mean for supplying fuel thereto,electrical spark ignition means for igniting said fuel to establish aflame, and means for controlling said fuel supplying means inresponse-to the presence of flame, said means including an electricdischarge device having an anode, a cathode, and a control electrode,said cathode being in electrical conducting relation with said fuelsupply means, and a first flame electrode positioned in the path of saidflame and electrically connected to said anode and a second flameelectrode positioned in the path of said flame intermediate said fuelsupply means and said first-flame electrode and connected to saidcontrol electrode.

3. In combination, a furnace having a combustion chamber, meansincluding a nozzle for supplying a combustible mixture to said chamberand propagating the same in a predetermined direction therein, meansincluding the transformer of the type having the midpoint of itssecondary grounded and ignition electrodes positioned in proximity tosaid nozzle for igniting said combustible mixture, and means forcontrolling said flrst mentioned means in response to the presence offlame, said means including an electric discharge device having acathode, an anode, and a control electrode, an electrical connectionfrom said cathode to said nozzle, a flame electrode electricallyconnected with said anode and positioned in the path of the flame, asecond flame electrode electrically connected to said control electrodeand positioned in the path of the flame at a position intermediate lastnamed flame electrode and the ignition electrodes and nozzle.

4. In combination, a furnace having a combustion chamber, means forsupplying a combustible mixture of air and oil to said combustionchamber and propagating the same in a predetermined direction therein,means including a transformer of the type having the midpoint of itssecondary grounded and ignition electrodes positioned in proximity tosaid mixture for igniting said combustible mixture, and means forcontrolling said first mentioned means in response to the pres ence offlame, said means including an electric discharge device having ananode, a control electrode and cathode, the latter being in electricalconducting relation with the combustible mixture, and flame electrodesconnected to said con- 7| trol electrode and anode positionedrespectively in the path of the flame at progressive distances from thepoint at which the combustible mixture enters the combustion chamber.

5. In combination, a furnace having a combustion chamber, electricallyoperated means for supplying a combustible mixture thereto, means forpropagating the combustible mixture and flame in a predetermineddirection in said chamber, means for igniting said mixture to establisha flame, an energizing circuit for said mixture supplying and ignitingmeans, and means for controlling the energization oi! said circuit inresponse to the presence of a flame within said combustion chamber, saidmeans including an electric discharge device having an anode, a cathode,and a control electrode, said cathode being in electrical conductingrelation with said combustible mixture propagating means, and a pair offlame electrodes progressively positioned in the direction oi. flamepropagation in the path of the flame, the flrst flame electrode beingconnected to said control electrode and the second flame electrode beingconnected to said anode.

6. In combination, means for supplying and projecting a combustiblemixture of air and oil in a predetermined direction, means for ignitingsaid mixture to establish a flame, and means responsive to the presenceof said' flame for controlling said first mentioned means, said meansincluding an electric discharge devlcehaving an anode, a cathode, and acontrol electrode, said cathode being in electrical conducting relationwith said combustible mixture projecting means, and means includingflame electrodes positioned in the flame and connected to the anode andcontrol electrode respectively, the flame electrode connected to thecontrol electrode being positioned between the flame electrode connectedto the anode and the point at which the combustible mixture isprojected.

'7. In combination, a furnace having a combustion chamber, meansincluding a nozzle for supplying a combustible mixture of air and oil tosaid combustion chamber and propagating the same in a predetermineddirection therein, said nozzle being electrically grounded, meansincluding a transformer having the midpoint of its secondary groundedand ignition electrodes posiresponse to the presence of flame, saidmeans including an electric discharge device having a control electrode,means for rendering said device normally non-conductive in the absenceof a flame, and means including a flame electrode adapted to collectsaid positive ions positioned in the path of the flame and electricallyconnected to the control electrode for substantially immediatelyrendering said electric discharge device conductive upon the occurrenceof flame.

8. In a control system, the combination including a furnace, means forsupplying a combustible mixture thereto, means for igniting said mixtureto establish a flame, means including a multi-element electric dischargedevice for controlling said flrst mentioned means in response to thepresence of flame, means including flame electrodes positioned in thepath of the flame and electrically connected to the elements of saiddischarge device establishing a conductive path through the flame forrendering said device connon-conductive upon the establishment ofconductive paths across said flame electrodes on the surface of orthrough said supporting means.

9. In combination means for supplying and igniting a combustible mixtureto establish a flame, an electric discharge device having a cathode, acontrol electrode and an anode, means including a plurality of flameelectrodes positioned in the path of a flame for rendering said deviceconductive upon the appearance of flame, supporting means for said flameelectrodes, and means for preventing the operation of said device uponthe occurrence of a leakage path across said flame electrodes on thesurface of or through said supporting means.

10. In combination, means for supplying and igniting a combustiblemixture to establish a flame, an electric discharge device having acathode, a control electrode, and an anode, means including a pluralityof flame electrodes electrically insulated from each other and groundpositioned in the path oi a flame and across which the flame establishesa conductive path for rendering said device conductive upon theappearance of the flame, and means for rendering said devicenonconductive upon the occurrence of a leakage path on the surface or orthrough the insulation across said flame electrodes or from said flameelectrodes to ground.

11. In a flame detector the combination including a multi-elementelectric discharge device having a cathode, a control electrode and ananode, means for applying a negative bias upon said control electrodesin the absence of flame, means for applying a positive bias on saidcontrol electrode to render said device conductive upon the appearanceof said flame, said means including a plurality of flame electrodeselectrically insulated from each other and ground having electricalincluding-means for applying a negative bias on said control electrodeduring the half cycle the discharge device normally would be operative.

12. In a flame detector, the combination including a multi-elementelectric discharge device having a cathode, a control electrode and ananode, means for applying a negative bias upon said control electrode inthe absence of flame, means for applying a positive bias on said controlelectrode to render said device conductive upon the appearance of saidflame, said means including a plurality of flame electrodes havingelectrical connections to elements of said discharge device and acrosswhich the flame establishes a conductive path, means for supporting saidflame means for applying a positive bias on said control electrode torender said device conductive upon the appearance of said flame, saidmeans including a plurality oi flame electrodes having electricalconnections to elements of said discharge device and so positioned inthe path of the flame that the latter establishes a conductive pathacross them, means for supporting said flame electrodes, and meansincluding a source of potential intermediate said flame electrodes forrendering said device non-conductive upon the occurrence of a leakagepath on the surface 01' or through said supporting means across saidflame electrodes.

14. In a flame responsive device, the combination including an electricdischarge device having an anode, control electrode and cathode, meansfor maintaining said device non-conductive in the absence 0! flame, andmeans for rendering said device conductive in the presence of flame,said means including electrical connections placing said cathode inelectrical conducting relation yith the flame and connections from thecontrol e e and anode to selected points in the path i the flame, theanode connection totheflamebeingatagreaterdistanceinthe direction offlame'propagation from the cathode connection than the control electrodeconnection.

ALVA L. BWII'I.

